Practical Magnetic and Electromechanical Design

This book is about developing an intuitive understanding of the magnetic fields in solenoids, actuators, transformers, inductors, sensors, and materials. It shows that armed only with a spreadsheet, one can quickly and accurately evaluate a wide array of magnetic designs. This book is written for students and practicing engineers involved in the design of magnetic and electromechanical devices. The material presented is a compilation of the practical approaches used over the author's 37-year career at Eaton Research Labs and is intended to help the reader gain a "feel" for locations and strengths of magnetic fields and an intuitive insight into what magnetic fields do and how to use them. This book makes magnetics easy to understand and practical to apply in magnetic research, experimentation, and analysis of magnetic fields encountered in engineering challenges. Accurate and reliable methods are presented for the design of magnetic sensors, actuators, controls, and other electromechanical devices with the notable exclusion of rotating machines that are well covered by various authors and courses in university Electrical Engineering departments. Actuators, solenoids, and magnetic sensors have been around in various forms for over a century, and they are critical components of control and protection systems including relays and circuit breakers. This book has a strong foundation in the methods developed by H. C. Roters with additional topics in the areas of permanent magnet materials and permanent magnet performance in particular. The methodologies also take full advantage of complex spreadsheet capabilities, as well as finite element analysis as a counterpart to the calculations. 

This book makes magnetics easy to understand and practical to apply in magnetic research, experimentation, and analysis of magnetic fields encountered in engineering challenges. Accurate and reliable methods are presented for the design of magnetic sensors, actuators, controls, and other electromechanical devices. This book has a strong foundation in the methods developed by H. C. Roters with additional topics in the areas of permanent magnet materials and permanent magnet performance. The methodologies also take full advantage of complex spreadsheet capabilities, as well as finite element analysis as a counterpart to the calculations. Design examples include calculations for losses and temperature rise, which are critical for all electromagnetic systems. The smallest design usually has the highest temperature rise. The best design usually considers the trade-off between size and temperature rise. The design calculations presented are practical in the sense that they can be quickly and accurately applied in a spreadsheet model using the permeance method (also known as reluctance method or magnetic circuit method). The permeance method evaluates the magnetic field from the perspective of a magnetic circuit, analogous to an electric circuit. Chapter 1 describes this in detail and aims to provide an understanding of magnetic flux paths based on the simple question, "If I were a magnetic flux line, where would I go?" The accuracy of the permeance method is demonstrated with comparisons to measurements and finite element simulations. Practical methods also address the issues of time and effort. Some ideas need only "feasibility" level accuracy, while other design-specific challenges require high-level accuracy. This relates directly to budget and schedule issues on engineering projects. Increased effort (model detail, complexity, size, time) is needed to achieve increased accuracy. The best strategic approach is to use a method that is quick and provides enough accuracy to make a valid design decision. A spectrum of calculation methods can be considered 1) a hand calculation, 2) a simple spreadsheet model, 3) a complex spreadsheet model, 4) a 2D or axisymmetric finite element model, 5) a 3D finite element model. A spreadsheet model can also be used to quickly determine the starting size for a finite element model. A critical step for gaining confidence in the validity of any analysis is to check the results against those of a simple calculation. In general, when doing a complex analysis (such as a finite element simulation), the first step should be a simple calculation (such as a spreadsheet calculation) and a visualization of the magnetic field. The finite element simulation results can then be quickly reviewed for the shape of the magnetic field and the magnitude of the flux density, current and force, to judge if the results are reasonable. Finite element models have many input values and boundary conditions that are prone to typographical errors (such as a decimal point error, or a dimensional units error). Errors can be quickly detected when compared to a simple calculation and magnetic field visualization. Chapter 2 discusses the mechanical force produced by actuators (reluctance force and Lorentz force), as a result of electromechanical energy conversion (the transfer of magnetic field energy into mechanical energy). Chapter 3 covers magnetic materials and highlights the relationship between magnetic properties (permeability, coercivity), crystal structure, and atomic spacing. Magnetic materials are critical in the performance of actuators and transformers. Chapters 4-8 address solenoid design, including coil design, coil temperature rise, solenoid dynamic performance, back EMF, and the use of rectification and shading to prevent zero flux and zero force in AC actuators. Chapters 9 and 10 discuss transformers, inductors, inductive current sensors, core loss, and BH magnetization curve measurement. Chapters 11 and 12 cover the topics of air-core coil inductance, the Biot-Savart law, and the force between coils and permanent magnets. High-speed actuators are discussed in chapters 13 and 14, including repulsion between current-carrying conductors and eddy currents, which are utilized in circuit breakers, slot motors, and Thomson coils. Chapter 15 gives a summary of magnetic field sensors, including position sensors and current sensors based on the magnetic field.

Mark is an electro-mechanical engineer with product experience in sensors, actuators, circuit breakers, contactors, mechanisms, hydraulic valve actuators, bimetal actuators, transformers, inductors, electronic packaging (cooling, vibration, shock), finite element magnetics and programming (Visual Basic, Fortran). He has experience working in both the manufacturing and research environments. His strengths include electromagnetics, mechanical dynamics, heat transfer, project management, team leading, mentoring, teaching, and the ability to apply physics to a wide range of engineering problems. Mark holds an MSME degree in heat transfer and fluid dynamics from the University of Wisconsin-Milwaukee, and a BSME degree from the University of Wisconsin-Madison with specialties in dynamic systems, kinematics, strain energy, and numerical optimization. During the past 37 years at Eaton Research Labs, he focused on designing magnetic and electromechanical devices, where he was granted 123 US and foreign patents. He also has 49 publications with 16 journal papers, 1 book chapter, and 1 book appendix, and has given 63 invited presentations. Mark's awards include; 1999 UWM Mechanical Engineering Department Alumni Award for Outstanding Achievement; 2006 Eaton Electrical Group Community Service Award; 2010 Engineers & Scientists of Milwaukee Engineer of the Year; 2013 UWM CEAS Meritorious Service Alumnus Award. Mark has been involved as a leader in the following organizations; 2003 – 2018 Chair of IEEE Magnetics Chapter for the Milwaukee Section; 2004 – 2009 Chair of UWM ME Department Industrial Advisory Council; 2007 Chair of Purdue University CTRC Industrial Advisory Board; Since 2009 Member of Board of Directors for the Kids from Wisconsin. Mark has taught courses in kinematics at MSOE and heat transfer, shock, and vibration in electronic systems at UWM. He also participates in many volunteer activities directed toward mentoring and encouraging students in the areas of science, technology, engineering, and math.